Most aircraft components are made of metal, making them susceptible to corrosion. From the time an aircraft is exposed to the elements, particularly damp, salty marine environments, corrosion becomes a concern. Even with the advent of better materials, staying on top of aircraft corrosion inspections and performing immediate repair and treatment of corroded areas is extremely important to ensure your aircraft is airworthy. Corrosion is the deterioration of metal by either chemical or electrochemical attack, and can take place on either internal or external surfaces. Corrosion typically changes the surface of your aircraft Airworthiness-Consulting, weakening the interior or loosening or damaging adjacent components. There are many factors that affect corrosion, including climate and foreign material, such as soil, oil, great, salt water, spilled battery acids, caustic cleaning solutions, welding and brazing flux residues. That is why continual inspections, prevention treatments and repairs are necessary parts of a good aircraft corrosion control program.

Aircraft Corrosion Inspection

There are two general classifications of corrosion – direct chemical attack and electrochemical attack. In both types, the metal is converted into a metallic compound such as an oxide, hydroxide or sulfate. Forms of corrosion include:

  • Surface
  • Dissimilar Metal
  • Intergranular
  • Stress
  • Fretting

To perform a thorough inspection, it is important to know what areas are most prone to corrosion. These include:

  • Exhaust Trail Areas
  • Battery Compartments and Battery Vent Openings
  • Bilge Areas
  • Wheel Well and Landing Gear
  • Water Entrapment Areas
  • Engine Frontal Areas
  • Cooling Air Vents
  • Wing Flap and Spoiler Recesses
  • External Skin Areas

Inspections should be performed daily, particularly on those aircraft that are on or near water. A detailed inspection will include the following steps:

  1. Thorough cleaning of the area being inspected.
  2. Perform a visual inspection with a magnifying glass.
  3. Remove paint from areas that are of concern.
  4. Perform a second visual inspection with a magnifying glass.
  5. Refer to the appropriate structural repair manual for damage limits.

It is important to consider prior metal loss, including metal on each side of the damage, when assessing corrosion damage. Upon completion of the aircraft corrosion inspection, any damage found must be evaluated. Typically the severity of corrosion damage is grouped as follows:

  • Light – scarred protective coating or light surface corrosion characterized by discoloration and pitting to a depth of approximately 1-mil maximum.
  • Moderate – similar to light except there are typically blisters of evidence or scaling and flaking. Pit depths may be as deep as 10 mils.
  • Severe – Often includes severe intergranular corrosion, blistering, scaling or flaking. Pit depths are deeper than 10 mils.
  • Repairable damage -Corrosion damage exceeds the limits of the MIM or SRM. The affected part may be used after repair.
  • Nonrepairable damage – damage exceeds established repair limits and must be replaced or require a special depot-level repair.

Aircraft Corrosion Repair and Treatment

Complete corrosion treatment involves cleaning and stripping the area, removing as much of the corrosion as practical, neutralizing any residual materials in pits and crevices, restoring protective surface films and applying temporary or permanent coatings or paint finishes. There are various blasting techniques that remove corrosion while leaving as much metal intact as possible, including:

  • Vapor
  • Soft-grit
  • Dry vacuum
  • Dry honing (the only approved method of removing corrosion on assembled aircraft)

If the corrosion is severe, then an abrasive wheel can be used. This device is meant to be used on thick metal and requires eye protection to be used at all times. All aircraft corrosion repairs must be made in accordance with the appropriate manuals while using proper measures to ensure the safety of the person making the repairs.

Aircraft Corrosion Control

While many improvements have been made to the materials and coatings used to protect aircraft from corrosion, developing a solid aircraft corrosion treatment and control program is an important part of every maintenance plan. Detailed daily inspections are needed, and all preventative maintenance programs should include:

  • Thorough rinsing and cleaning to remove salt and other corrosive agents. Pay special attention to exposed areas such as landing gear.
  • Periodic lubrication to seal the metal against moisture.
  • Immediate treatment of corrosion and touchup of damaged paint areas.
  • Keep drain holes free of blockage.
  • Drain fuel cell sumps daily.
  • Wipe down exposed critical areas every day.
  • Seal aircraft against water for protection during foul weather,
  • Proper ventilation of aircraft to prevent moisture from gathering.
  • Use protective covers on parked aircraft, particularly during inclement weather.

Aircraft corrosion repair can be very costly, particularly if the corrosion goes unnoticed for a period of time. Developing an aircraft corrosion control program that includes appropriate inspections, treatments and timely repairs will save time, money and ensure the safety of your aircraft while in flight.

Global Aircraft Service was founded by Greg Katonica and Paul McCain in 1998. Both have many years of experience in Fuel System Repairs. We are based at 4500 Claire Chennault, Addison, Texas 75001. We have a large facility that can accommodate most medium size corporate aircraft or we will travel Airworthiness-Consulting to any site in the World.